This apparatus is directed to a device to be placed in a drill stem at the time that the drill stem is pulled from the well borehole during drilling and, more particularly, is a device for weighting the column of mud in the drill stem. This is a continuation-in-part of U.S. Pat. No. 4,923,011 issued on May 8, 1990 which is incorporated by reference.
During drilling of a well, it is necessary to periodically remove the drill stem from the borehole, typically to replace the drill bit. When this occurs, the drill stem is normally lifted up and disassembled joint by joint or perhaps stand by stand. In the process of removing the pipe from the borehole, it is normally lifted in a wet condition and, upon unthreading, may spill drilling fluid on the rig floor creating a risky condition. Moreover, this destroys the hydrostatic balance which existed in the borehole. Heretofore, this has been overcome by slugging the column of mud in the drill stem with a slug of drilling fluid of heavier density so that it will tend to keep the level of mud down in the drill pipe due to the hydrostatic unbalance created on slugging. In the case of oil base muds, it requires the addition of weight material which has to be removed for best results when drilling is resumed.
The apparatus set forth in the parent disclosure hereof is thought to be a successful device which provides the necessary wiping inside the drill stem. This disclosure, however, sets out a further improvement which is directed to the resilient sleeve 25. In the referenced parent disclosure, the sleeve 25 is a resilient sleeve which is supported between upper and lower rings 27 and 28. It is made of resilient material so that it can flex and it tends to inflate, bowing outwardly to create a contact area which tends to wipe the inside of the pipe. Ordinarily, it provides contact against the full circle of the surrounding or enclosing axial passage through the drill stem. There are, however, internal upsets which are encountered periodically along the drill stem. When they are encountered, this requires the sleeve to contact against the upset regions, thereby shrinking to prevent leakage past the upset region. The present improvement sets forth a method and apparatus for further assuring that the sleeve is expanded radially outwardly so that the sleeve maintains more reliable contact with the surrounding drill stem, in particular better contact with the surrounding drill stem. Thus dynamically, the device will pass downwardly in a drill stem, being forced to shrink or narrow on encountering the internal upset, and is freed to expand radially outwardly after passing through the upset so that the present apparatus provides a more sure and certain contact region just below the upset. It is very helpful to maintain the resilient sleeve 25 at a fully inflated condition for assuring contact against the surrounding upset and the sidewall just below the upset. In the absence of certain contact, it is possible for leakage to occur and this system overcomes that tendency.
The present system has the further advantage of overcoming the tendency to leak by assuring a fully inflated sleeve during traversing of a drill stem. Moreover, the sleeve is filled with an incompressible fluid which is momentarily compressed when passing through an internal upset which fluid overflows from the sleeve into a chamber. The chamber is maintained under pressure which is assured by a cylinder in the chamber exposed to ambient pressure. Pressure on the tool dynamically moves the piston within the cylinder to adjust pressure equalization within the sleeve. This change in piston location maintains fluid pressure within the tool keeping the sleeve expanded in light of its physical location relative to upsets of the drill stem.
The present apparatus sets out an elongate tool which is buoyantly carried on the top of the mud column in the drill stem as the stem is being pulled and which includes a central elongate mandrel. The mandrel is of relatively narrow diameter to receive thereon a telescoped and slideable resilient sleeve. The resilient sleeve is not shaped as a cup, but rather incorportes upper and lower ends which are relatively narrow and are mounted on circular rings to enable telescoping movement of each end independently on the mandrel. The sleeve bows outwardly at the central portions and defines a resilient wiping surface. This surface is able to pass through the internal upset pipe. When it does, the sleeve is constricted slightly, forcing the two ends farther apart and which are both free to move. The two ends of the sleeve are arranged in a circular construction around the mandrel. Conveniently, shoulders at the upper and lower ends of the sleeve supported by the mandrel define the centered sleeve position, but such sleeve movement is nevertheless permitted during transition through an internal upset. The transition thus occurs as the device is traveling through the drill stem and yet permits the sleeve to slide through the internal upset, shrinking at the fatter central portion, forcing the two ends thereof relatively apart, and moving at one end or the other to accommodate appropriate elongation on diametric shrinkage, and further restoring to the original shape after transition through the internal upset. This is markedly different from cups which face upwardly or downwardly. Likewise, it is different from sleeves of substantially uniform diameter, and is substantially different from the wiping action provided by such devices.
The foregoing briefly sets out certain aspects of the present disclosure, but details of the present apparatus will become more readily apparent and understood in conjunction with the drawings of the preferred embodiment, and it is therefore a structure including the components illustrated discussed below for the preferred embodiment.